Fix #181 by dropping `exit(1)` (#182)

Seems that Lwt 5 throws a weird error when using `exit(1)` inside a
promise. So instead of exiting in the command, making all executable
modules a function that returns a `result((), status_code)` is a better fit.

Relates to: https://github.com/ocsigen/lwt/issues/758

executable/Alias.re

@@ -16,9 +16,8 @@ let run = (~name, ~version) => {
         versionPath
       </Pastel>,
     );
-    exit(1);
-  };
-
+    Lwt.return_error(1);
+  } else {
     Logger.info(
       <Pastel>
         "Aliasing "
@@ -30,5 +29,6 @@ let run = (~name, ~version) => {
 
     let%lwt () = Versions.Aliases.set(~alias=name, ~versionPath);
 
-  Lwt.return();
+    Lwt.return_ok();
+  };
 };

executable/Env.re

@@ -158,5 +158,5 @@ let run =
     printUseOnCd(~shell) |> Console.log;
   };
 
-  Lwt.return();
+  Lwt.return_ok();
 };

executable/FnmApp.re

@@ -1,14 +1,23 @@
 let version = Fnm.Fnm__Package.version;
 
+let runCmd = lwt => {
+  lwt
+  |> Lwt_main.run
+  |> (
+    fun
+    | Error(err_code) => exit(err_code)
+    | Ok () => ()
+  );
+};
+
 module Commands = {
-  let use = (version, quiet) => Lwt_main.run(Use.run(~version, ~quiet));
-  let alias = (version, name) => Lwt_main.run(Alias.run(~name, ~version));
-  let default = version =>
-    Lwt_main.run(Alias.run(~name="default", ~version));
-  let listRemote = () => Lwt_main.run(ListRemote.run());
-  let listLocal = () => Lwt_main.run(ListLocal.run());
-  let install = version => Lwt_main.run(Install.run(~version));
-  let uninstall = version => Lwt_main.run(Uninstall.run(~version));
+  let use = (version, quiet) => Use.run(~version, ~quiet) |> runCmd;
+  let alias = (version, name) => Alias.run(~name, ~version) |> runCmd;
+  let default = version => Alias.run(~name="default", ~version) |> runCmd;
+  let listRemote = () => ListRemote.run() |> runCmd;
+  let listLocal = () => ListLocal.run() |> runCmd;
+  let install = version => Install.run(~version) |> runCmd;
+  let uninstall = version => Uninstall.run(~version) |> runCmd;
   let env =
       (
         isFishShell,
@@ -19,7 +28,6 @@ module Commands = {
         useOnCd,
         logLevel,
       ) =>
-    Lwt_main.run(
     Env.run(
       ~forceShell=Fnm.System.Shell.(isFishShell ? Some(Fish) : shell),
       ~multishell=isMultishell,
@@ -27,8 +35,8 @@ module Commands = {
       ~fnmDir,
       ~useOnCd,
       ~logLevel,
-      ),
-    );
+    )
+    |> runCmd;
 };
 
 open Cmdliner;

executable/Install.re

@@ -123,7 +123,7 @@ let main = (~version as versionName) => {
       Lwt.return_unit;
     };
 
-  Lwt.return();
+  Lwt.return_ok();
 };
 
 let run = (~version) =>
@@ -139,7 +139,7 @@ let run = (~version) =>
         <Pastel color=Pastel.Cyan> {System.NodeArch.toString(arch)} </Pastel>
       </Pastel>,
     );
-    exit(1);
+    Lwt.return_error(1);
   | Versions.Version_not_found(version) =>
     Logger.error(
       <Pastel>
@@ -148,7 +148,7 @@ let run = (~version) =>
         " not found!"
       </Pastel>,
     );
-    exit(1);
+    Lwt.return_error(1);
   | VersionListingLts.Problem_with_finding_latest_lts(
       VersionListingLts.Cant_find_latest_lts,
     ) =>
@@ -163,5 +163,5 @@ let run = (~version) =>
         reason
       </Pastel>,
     );
-    exit(1);
+    Lwt.return_error(1);
   };

executable/ListLocal.re

@@ -31,12 +31,13 @@ let main = () =>
            Console.log(<Pastel ?color> "* " {version.name} aliases </Pastel>);
          });
 
-      Lwt.return();
+      Lwt.return_ok();
     }
   );
 
 let run = () =>
   try%lwt(main()) {
   | Cant_read_local_versions =>
-    Console.log("No versions installed!") |> Lwt.return
+    Console.log("No versions installed!");
+    Lwt.return_ok();
   };

executable/ListRemote.re

@@ -22,5 +22,5 @@ let run = () => {
        Console.log(<Pastel ?color> str </Pastel>);
      });
 
-  Lwt.return();
+  Lwt.return_ok();
 };

executable/Uninstall.re

@@ -17,7 +17,7 @@ let run = (~version) => {
         " is not installed."
       </Pastel>,
     );
-    exit(1);
+    Lwt.return_error(1);
   | Some(installedVersion) =>
     Logger.debug(
       <Pastel>
@@ -37,6 +37,6 @@ let run = (~version) => {
         " has correctly been removed."
       </Pastel>,
     );
-    Lwt.return_unit;
+    Lwt.return_ok();
   };
 };

executable/Use.re

@@ -92,7 +92,8 @@ let main = (~version as providedVersion, ~quiet) => {
     | Some(version) => Lwt.return(version)
     | None => Dotfiles.getVersion()
     };
-  switchVersion(~version, ~quiet);
+  let%lwt () = switchVersion(~version, ~quiet);
+  Lwt.return_ok();
 };
 
 let rec askIfInstall = (~version, ~quiet, retry) => {
@@ -107,7 +108,9 @@ let rec askIfInstall = (~version, ~quiet, retry) => {
     let%lwt _ = Install.run(~version);
     retry(~version, ~quiet);
   | "N"
-  | "n" => Lwt_io.write_line(Lwt_io.stderr, "not installing!")
+  | "n" =>
+    let%lwt () = Lwt_io.write_line(Lwt_io.stderr, "not installing!");
+    Lwt.return_ok();
   | _ =>
     let%lwt _ =
       Lwt_io.write_line(Lwt_io.stderr, "Invalid response. Please try again:");
@@ -128,7 +131,7 @@ let rec run = (~version, ~quiet) =>
     if (Fnm.Config.FNM_INTERACTIVE_CLI.get()) {
       askIfInstall(~version, ~quiet, run);
     } else {
-      exit(1);
+      Lwt.return_error(1);
     };
   | Dotfiles.Conflicting_Dotfiles_Found(v1, v2) =>
     error(
@@ -142,7 +145,7 @@ let rec run = (~version, ~quiet) =>
         v2
       </Pastel>,
     );
-    exit(1);
+    Lwt.return_error(1);
   | Dotfiles.Version_Not_Provided =>
     error(
       ~quiet,
@@ -150,5 +153,5 @@ let rec run = (~version, ~quiet) =>
         "No .nvmrc or .node-version file was found in the current directory. Please provide a version number."
       </Pastel>,
     );
-    exit(1);
+    Lwt.return_error(1);
   };